Abstract: An image forming apparatus which enables resolution modes to be readily changed over has a light-emitting element for irradiating a polygonal mirror with a light beam and a controller for controlling the light-emitting element. The controller is connected to an image clock signal changeover circuit that changes the period of an image clock signal to a period which is n (a positive integer) times the former. The controller is arranged such that the image recording density in the horizontal scanning direction can be changed by the image clock signal changeover circuit and/or the controller judges the pulses of a horizontal synchronizing signal output from a photosensor to be valid at intervals of (n-1) pulses, thereby enabling control of the recording density in the vertical scanning direction.

Abstract: A developing device for use in an electrophotographic printer comprises a non-magnetic cylindrical developing sleeve for conveying magnetic toner on its surface in rotating condition, a toner supply unit for supplying the magnetic toner onto the developing sleeve, a fixed magnetic field generating member disposed inside the developing sleeve, and a doctor blade unit disposed in confronting relation to the surface of the developing sleeve for regulating the layer thickness of the magnetic toner. The doctor blade unit includes a pair of magnetic pole plates whose distal ends are spaced a given distance from each other and magnetized as to exhibit opposite magnetic polarities. The fixed magnetic field generating member has a notch formed in a section facing the magnetic pole plates such that its magnetic flux does not act virtually on the magnetic pole plates.